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28-Oct-2010

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American Association for the Advancement of Science

An early tool-making technique



Click here for a 360-degree view of Blombos Cave. (QuickTime required.)
Graphic courtesy of C. Henshilwood and M. Haaland

A technique for shaping stones into sharp-edged points may have emerged about 55,000 years earlier than scientists have previously thought, according to a study of stone tools from a cave in South Africa called Blombos Cave.

Previously, researchers have also found other evidence of "modern" human behavior, such as shell beads, from this 75,000-year-old cave site, where new ideas and techniques may have been rapidly introduced.



Experimental knapping of silcrete, shown here by Dr. V. Mourre. using a stone hammer (hard hammer percussion). This photo was taken at Iziko Museum, Cape Town, September 2007.
Image courtesy of C. Thiébaut

The tool-making technique, called pressure flaking, involves using an animal bone or some other object to exert pressure near the edge of a stone piece and carve out a relatively small flake. A tool-maker would typically first strike a stone with hammer-like tools to give the piece its initial shape; then they would use pressure-flaking to refine the blade's edges and shape its tip. The technique has been considered a fairly recent innovation, arising about 20,000 years ago.

Vincent Mourre of INRAP Méditerranée and Université de Toulouse-Le Mirail in France and his coauthors analyzed some silcrete stone points from Blombos Cave that were probably tied to spears and used as hunting weapons.

The researchers analyzed the points in microsopic detail and compared them to points that they made themselves, by heating and pressure-flaking silcrete that they collected from outcrops near Blombos Cave. The similarities between the artifacts and the modern recreations suggest that the tool-makers of Blombos Cave used pressure-flaking about 75,000 years ago.

The authors speculate that a flexible approach to technology in this region may have benefited the groups of humans that migrated out of Africa after roughly 60,000 years ago.

This research appears in the 29 October issue of the journal Science.

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